The present invention relates to a polycarbonate resin for an optical disk substrate and an optical disk substrate, and more particularly, it relates to a polycarbonate resin that is suitable for a material of an optical disk substrate having less defects due to flash, and an optical disk substrate formed with the resin.
A polycarbonate resin is widely used as a substrate of an optical disk, such as CD, CD-ROM, MO, CD-R, CD-RW, DVD-ROM, DVD-R and DVD-RAM, owing to the transparency, the heat resistance and the low water absorbing property thereof. In general, these optical disks are often produced by such a process that a surface formed by engraving signals, such as pits and grooves, on a thin plate of nickel called as a stamper arranged in a metallic mold is transferred to a substrate formed with a polycarbonate resin through injection molding.
In the production of a substrate of an optical disk in recent years, several tens to a number exceeding one hundred of molding machines are introduced in one factory to further enhance the mass production volume efficiency, and simultaneously quality control is severely ensured. However, although there is no change of a stamper or no change in molding conditions, and the factors determining the flowability of a polycarbonate resin, such as the molecular weight, the molecular weight distribution, the glass transition temperature and the like, are stable within prescribed ranges, there are some cases where releasing failure extemporaneously occurs upon sprue cutting of a center hole of a disk substrate, and the outer circumference of the disk substrate or fine flash formed on the outer circumference is in friction with a metallic mold due to the releasing failure to cause contamination of resin dusts, whereby the yield of the disk substrates is decreased to several percents to several tens percents. The phenomenon is generally referred to as a defect due to flash, which can be prevented by increasing an amount of a releasing agent. However, the amount of the releasing agent cannot be increased to an unnecessary level because there is a tendency of occurrence of defects on optical characteristics, particularly such a tendency that occurrence of defects of polarization and white turbidity in the polycarbonate resin is accelerated upon an accelerated aging test under constant temperature and humidity, whereby the reliability of storage stability of recorded data as an optical disk is also lowered.
The invention has been developed under the circumstances, and is to provide a polycarbonate resin that is suitable for a material of an optical disk substrate having less defects due to flash without increase of an addition amount of a releasing agent to an unnecessary level, and an optical disk substrate formed with the resin.
As a result of various investigations made by the inventors, it has been found that occurrence of defects due to flash is correlated with (1) an amount of iron and a free total phenol content in a polycarbonate resin, (2) the particular impurities in 2,2-(4-hydroxyphenyl)propane as a raw material and a fraction of hydroxyl end groups in the polycarbonate resin, (3) an iron amount and a 1H-NMR spectrum of the polycarbonate resin, and (4) an iron amount and a fraction of hydroxyl end groups in the polycarbonate resin, and thus the first invention to the fourth invention have been completed.
That is, the first invention will be outlined below.
1. A polycarbonate resin for an optical disk substrate characterized by having a viscosity average molecular weight of from 10,000 to 17,000, an iron content of 0.2 ppm or less and a free total phenol content of 80 ppm or less, and containing from 100 to 500 ppm of a releasing agent.
2. A polycarbonate resin for an optical disk substrate described in the item 1, which has an acetone soluble content of 12% by mass or less.
3. A polycarbonate resin for an optical disk substrate described in the item 1 or 2, which contains from 150 to 350 ppm of a releasing agent.
4. A polycarbonate resin for an optical disk substrate described in one of the items 1 to 3, wherein the releasing agent is a polyhydric alcohol fatty acid ester.
5. An optical disk substrate comprising a polycarbonate resin for an optical disk substrate described in one of the items 1 to 4.
The second invention will be outlined below.
1. A polycarbonate resin for an optical disk substrate characterized by being produced with, as a raw material, 2,2-(4-hydroxyphenyl)propane (hereinafter referred to as bisphenol A) having a content of 2-(2-hydroxylphenyl)-2-(4-hydroxylphenyl)propane (hereinafter referred to as 2,4-bisphenol A) of 1,000 ppm or less, a content of a cyclic dymer of p-isopropenylphenol represented by the following general formula (I) (hereinafter referred to as a cyclic IPP dimer) of 150 ppm or less: 
and a content of a trisphenol compound represented by the following general formula (II) (hereinafter simply referred to as a trisphenol) of 150 ppm or less: 
having a viscosity average molecular weight of from 10,000 to 17,000 and a fraction of hydroxyl end groups of less than 7% by mole, and containing from 100 to 500 ppm of a releasing agent.
2. A polycarbonate resin for an optical disk substrate as described in the item 1, which has a free total phenol content of 80 ppm or less.
3. A polycarbonate resin for an optical disk substrate described in the item 1 or 2, which contains from 150 to 350 ppm of a releasing agent.
4. A polycarbonate resin for an optical disk substrate described in one of the items 1 to 3, wherein the releasing agent is a polyhydric alcohol fatty acid ester.
5. An optical disk substrate comprising a polycarbonate resin for an optical disk substrate described in one of the items 1 to 4.
The third invention will be outlined below.
1. A polycarbonate resin for an optical disk substrate characterized by satisfying the following conditions:
(1) a viscosity average molecular weight is from 10,000 to 17,000,
(2) an iron content is 0.2 ppm or less;
(3) when an intensity of a chemical shift xcex4 of from 7.0 to 7.5 ppm based on a phenyl ring in a spectrum measured with 1H-NMR is 1,000, signal intensities at xcex4 of from 1.02 to 1.08 and from 6.69 to 6.73 are 0.01 or less; and
(4) from 100 to 500 ppm of a releasing agent is contained.
2. A polycarbonate resin for an optical disk substrate as described in the item 1, which contains from 150 to 350 ppm of a releasing agent.
3. A polycarbonate resin for an optical disk substrate described in the item 1 or 2, wherein the releasing agent is a polyhydric alcohol fatty acid ester.
4. A polycarbonate resin for an optical disk substrate described in the item 3, wherein the polyhydric alcohol fatty acid ester is a fatty acid monoester of glycerin.
5. An optical disk substrate comprising a polycarbonate resin for an optical disk substrate described in one of the items 1 to 4.
The fourth invention will be outlined below.
1. A polycarbonate resin for an optical disk substrate characterized by having a viscosity average molecular weight of from 10,000 to 17,000, an iron content of 0.2 ppm or less and a fraction of hydroxyl end groups of less than 7% by mole, and containing from 100 to 500 ppm of a releasing agent.
2. A polycarbonate resin for an optical disk substrate as described in the item 1, which contains from 150 to 350 ppm of a releasing agent.
3. A polycarbonate resin for an optical disk substrate described in the item 1 or 2, wherein the releasing agent is a polyhydric alcohol fatty acid ester.
4. A polycarbonate resin for an optical disk substrate described in the item 3, wherein the polyhydric alcohol fatty acid ester is a fatty acid monoester of glycerin.
5. An optical disk substrate comprising a polycarbonate resin for an optical disk substrate described in one of the items 1 to 4.